Wafer-level underfill and over-molding

ABSTRACT

A mold includes a top portion, and an edge ring having a ring-shape. The edge ring is underlying and connected to edges of the top portion. The edge ring includes air vents. The edge ring further encircles the inner space under the top portion of the mold. A plurality of injection ports is connected to the inner space of the mold. The plurality of injection ports is substantially aligned to a straight line crossing a center of the top portion of the mold. The plurality of injection ports has different sizes.

BACKGROUND

In the packaging of integrated circuits, package components, such asdevice dies and package substrates, are typically stacked through flipchip bonding. To protect the solder regions between the stacked packagecomponents, an underfill is disposed between the stacked packagecomponents. A molding compound may then be molded on the stacked packagecomponents through over-molding.

The conventional molding methods include compression molding andtransfer molding. Compression molding may be used for the over-molding.Since the compression molding cannot be used to fill the underfill intothe gaps between the stacked dies, the underfill needs to be dispensedin separate steps other than the compression molding. On the other hand,transfer molding may be used to fill a molding underfill into the gapbetween, and over, the stacked package components. Accordingly, transfermolding may be used to dispense the underfill and the molding compoundin the same process step. Transfer molding, however, cannot be used onthe packages including round wafers due to non-uniform dispensing of themolding compound.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1A and 1B illustrate cross-sectional views of apparatuses inaccordance with exemplary embodiments, wherein the apparatuses are usedfor performing a wafer-level molding;

FIGS. 1C and 1D are a top view and a perspective view, respectively, ofthe apparatuses shown in FIGS. 1 A and 1B; and

FIGS. 2A and 2B illustrate a top view and a perspective view,respectively, of the apparatuses in accordance with alternativeembodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare illustrative, and do not limit the scope of the disclosure.

An apparatus for wafer-level molding and the method of performing thewafer-level molding are provided in accordance with various exemplaryembodiments. The variations of the embodiments are discussed. Throughoutthe various views and illustrative embodiments, like reference numbersare used to designate like elements.

FIGS. 1A and 1B illustrate cross-sectional views of a wafer-levelmolding process. Referring to FIG. 1A, package structure 10 is placed inmold 26. Package structure 10 includes wafer 20, and dies 22 bonded towafer 20. In some embodiments, wafer 20 is a device wafer, whichincludes a plurality of device chips including active devices (such astransistors) therein. In alternative embodiments, wafer 20 is aninterposer wafer, which is free from active devices therein. Wafer 20may, or may not, include passive devices such as resistors, capacitors,and inductors, therein. The top view of wafer 20 may be rounded, forexample, as shown in FIG. 1C, although wafer 20 may have other top viewshapes. Dies 22 may be device dies including active devices therein.Alternatively, dies 22 may be packages including stacked dies.

Mold 26 includes top portion (a cover) 26A, which may have a roundtop-view shape (FIG. 1C). As shown in FIG. 1A, the top surfaces of dies22 are spaced apart from top portion 26A of mold 26 by a space. Mold 26further includes edge ring 26B, which encircles dies 22. Edge ring 26Bis connected to, and extends down from, the edges of top portion 26A.Edge ring 26B encircles a region underlying top portion 26A, whichregion is referred to as the inner space of mold 26 hereinafter. Mold 26may be formed of steel, stainless steel, ceramic, or the like. In someembodiments, as shown in FIG. 1A, mold 126, which is a lower mold, maybe placed under mold 26. Molds 26 and 126 are used in combination formolding package 10. In alternative embodiments, as shown in FIG. 1B, thebottom edge of edge ring 26B is placed on the edge portions of wafer 20.In these embodiments, no lower mold is needed.

As shown in FIGS. 1A and 1B, one or a plurality of injection ports 30 isdisposed to penetrate through top portion 26A of mold 26. Moldingmaterial 34 is injected into mold 26 through injection ports 30.Portions of molding material 34 flow into the gaps between dies 22.These portions of molding material 34 may perform the function of anunderfill. In addition, portions of molding material 34 flow into thegaps between dies 22, and into the space between dies 22 and top portion26A of mold 26. These portions of molding material 34 are used forover-molding. Accordingly, as shown in FIGS. 1A and 1B, the underfilldispensing and the over-molding are performed in the same step. Moldingmaterial 34 may be a molding underfill or another other type of polymerthat can be used for molding.

Edge ring 26B of mold 26 includes a plurality of air vents 32, which arethrough holes connecting the inner space of mold 26 to the externalspace. Air vents 32 are used to allow the venting of the air in theinner space of mold 26. Air vents 32 may be distributed throughout edgering 26B. In some embodiments, air vents 32 are used to vacuum the innerspace of mold 26, so that it is easy for molding material 34 to flowfrom the center of mold 26 to the edge. With the venting/vacuumingthrough air vents 32, it is less likely to have air bubbles formed inthe resulting dispensed molding material 34.

FIG. 1C illustrates a top view of the apparatus in FIGS. 1A and 1B. Insome embodiments, mold 26 has a top-view shape similar to the top-viewshape of wafer 20. The top portion of mold 26 may be rounded, and hascenter 38, which may also be substantially aligned to the center ofwafer 20. Injection ports 30 are denoted as 30-1 through 30-n, whereininteger n may be any suitable number. Throughout the description,injection ports 30 that are closer to center 38 are referred to as innerports, and injection ports 30 that are farther away from center 38 arereferred to as outer ports. It is appreciated that the terms “inner” and“outer” are relative to each other. For example, injection port 30-2 isan outer port when compared to injection port 30-1, and is an inner portwhen compared to injection port 30-3. Injection port 30-1 is closest tocenter, and hence is referred to as center port 30-1 hereinafter.Injection ports 30-n are closest to the edge of mold 26, and arereferred to as edge ports hereinafter.

In some embodiments, injection ports 30 are substantially aligned tostraight line 31, which crosses center 38 of the top portion 26A ofround mold 26. Molding material 34 (FIG. 1A) is injected into mold 26through the plurality of injection ports 30, and flows to the edge ofmold 26. In some embodiments, size W1, which may be a diameter or alength/width, of center port 30-1 is greater than size Wn of edge ports30-n. Ratio W1/Wn may be greater than 1, and may also be greater thanabout 5. Injection ports 30-1 through 30-n may also have increasinglysmaller sizes, and each of the outer ports may have a size smaller thanits inner ports. Accordingly, more molding material 34 is injectedthrough injection ports 30 that are closer to center 38 than the moldingmaterial 34 that is injected through injection ports 30 that are closerto the edges of mold 26. The portion of molding material 34 injectedthrough center port 30-1 needs to travel a greater distance (and fill agreater space) than the portion of molding material 34 injected throughedge ports 30-n. Accordingly, by designing injection ports 30 withdifferent sizes, the portions of molding material 34 injected throughdifferent injection ports 30 may flow (in the direction of the arrows inFIG. 1C) to the edge of mold 26 at substantially the same time. Thepossibility of the formation of voids in molding material 34 is thusreduced.

In some exemplary embodiments, molding material 34 may be injectedthrough injection ports 30 simultaneously. In alternative embodiments,molding material 34 is injected from different injection ports 30 atdifferent times. In some exemplary embodiments, center port 30-1 startsinjecting molding material 34 first, while other injection ports 30 lagbehind in injecting than the respective inner ports. Edge ports 30-n maystart injecting at a time after all the inner injection ports 30 havestarted injecting. In some exemplary embodiments, the staring injectiontime of edge ports 30-n may lag the starting injection time of centerport 30-1 by a time difference greater than about 70 seconds.

FIGS. 1A through 1C also illustrate molding dispenser 40, which isconnected to injection ports 30, and is configured to conduct moldingmaterial 34 to injection ports 30. Molding dispenser 40 includescontroller 41, which is configured to control the timing of theinjection through different ports 30.

FIG. 1D illustrates a perspective view of the structures shown in FIGS.1A through 1C. In some embodiments, air vents 32 (including 32-1 through32-m) have a uniform size, wherein the sizes may be the diameters or thelengths/widths, depending on the shapes of air vents 32. In alternativeembodiments, air vents 32 have different sizes depending on wherein therespective air vents 32 are located. For example, air vent 32-1 isfarthest from injection ports 30 and from line 31, to which injectionports 30 are aligned. Air vent 32-1 may have the greatest size W1′ amongall sizes of air vents 32. Air vent 32-m, which are closest to injectionports 30 and line 31, may have the smallest size Wm′. Air vents 32-1through 32-m may have increasingly smaller sizes. In some embodiments,ratio W1′/Wm′ may be greater than 1, or greater than about 5. Throughair vents 32, the inner space inside mold 26 may be vacuumed. Forexample, pipes (not shown) may be connected to air vents 32, and thevacuuming may be performed through the pipes. Alternatively, as shown inFIGS. 1A and 1B, the entire mold 26 may be placed in vacuumedenvironment 36, so that all air vents 32 are used for vacuuming theinner space of mold 26 at the same time. In the embodiments whereinvacuumed environment 36 is provided, no pipe needs to be connected toindividual air vents 32. With the air vents 32 having different sizes,molding material 34 may be dispensed more uniformly throughout wafer 20.

FIGS. 2A and 2B illustrate a top view and a perspective view,respectively, of the apparatus used for the wafer-level molding inaccordance with alternative embodiments. Unless specified otherwise, thematerials and the processes in these embodiments are essentially thesame as the like components, which are denoted by like referencenumerals in the embodiment shown in FIGS. 1A through 1D. The details ofthe embodiments shown in FIGS. 2A and 2B may thus be found in thediscussion of the embodiments shown in FIGS. 1A through 1D. Referring toFIG. 2A, the plurality of ports 30-1 through 30-n may be distributed toalign to straight lines 31 and 33, which are perpendicular to eachother. Both straight lines 31 and 33 may cross center 38 of mold 26.Similar to the embodiments in FIGS. 1A through 1D, injection ports 30that are closer to center 38 may have greater sizes than injection ports30 that are farther away from center 38. Furthermore, molding material34 may be injected through inner injection ports 30 earlier than throughthe respective outer injection ports 30.

FIG. 2B illustrates a perspective view of the apparatus in FIG. 2A. Insome embodiments, air vents 32 have a uniform size. In alternativeembodiments, air vents 32 have different sizes. For example, air vents32-1, which are farthest from injection ports 30 and lines 31 and 33,may have the greatest sizes, while air vents 32-m, which are closest toinjection ports 30 and lines 31 and 33, may have the smallest sizes.

In the embodiments, through the adjustment of the sizes of the injectionports, the sizes of the air vents, and/or the starting times of theinjection through different injection ports, the molding material may bedispensed at a greater rate to the center of the package than to theedge portions. Accordingly, a more uniform molding may be achieved.

In accordance with embodiments, a mold includes a top portion, and anedge ring having a ring-shape. The edge ring is underlying and connectedto edges of the top portion. The edge ring includes air vents. The edgering further encircles the inner space under the top portion of themold. A plurality of injection ports is connected to the inner space ofthe mold. The plurality of injection ports is substantially aligned to astraight line crossing a center of the top portion of the mold. Theplurality of injection ports has different sizes.

In accordance with other embodiments, a mold includes a top portionhaving a round edge, and an edge ring connected to the round edge of thetop portion. The top portion and the edge ring of the mold define aninner space therein. A plurality of air vents penetrates through theedge ring of the mold, wherein the plurality of air vents have differentsizes. A center injection port penetrates through the top portion of themold and connected to the inner space of the mold. The center injectionport is substantially aligned to the center of the top portion of themold.

In accordance with yet other embodiments, a method includes providing amold including a top portion, and an edge ring underlying and connectedto the top portion. The edge ring encircles an inner space underlyingthe top portion. A package structure is placed into the inner space. Thepackage structure includes a wafer, and a plurality of dies bonded tothe wafer. At a first time, a molding material starts to be injectedinto the inner space from a first injection port that penetrates throughthe top portion of the mold. At a second time later than the first time,the molding material starts to be injected into the inner space from asecond injection port that penetrates through the top portion of themold. The second injection port is farther away from a center of the topportion of the mold than the first injection port.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. An apparatus comprising: a mold comprising: a topportion; and an edge ring having a ring-shape, wherein the edge ring isunderlying and connected to edges of the top portion, wherein the edgering comprises air vents, and wherein the edge ring encircles an innerspace under the top portion; and a first plurality of injection portsconnected to the inner space of the mold, wherein the first plurality ofinjection ports is substantially aligned to a first straight linecrossing a center of the top portion of the mold, and wherein the firstplurality of injection ports has different sizes.
 2. The apparatus ofclaim 1 further comprising a dispenser connected to the first pluralityof ports, wherein the dispenser is configured to inject a moldingmaterial into the inner space of the mold through the first plurality ofports.
 3. The apparatus of claim 2, wherein the dispenser is configuredto start dispensing the molding material through different ones of thefirst plurality of injection ports at different times.
 4. The apparatusof claim 1, wherein the top portion has a round top-view shape, whereinthe first plurality of injection ports comprises a center port close tothe center, and an edge port farther away from the center than thecenter port, and wherein the center port has a size greater than a sizeof the edge port.
 5. The apparatus of claim 4, wherein from the centerto an edge of the top portion of the mold, the first plurality ofinjection ports has increasingly smaller sizes.
 6. The apparatus ofclaim 1, wherein the air vents have different sizes.
 7. The apparatus ofclaim 6, wherein a first air vent among the air vents has a greater sizethan a second air vent among the air vents, and wherein the first airvent is farther away from the first straight line than the second airvent.
 8. The apparatus of claim 1 further comprising a second pluralityof injection ports connected to the inner space of the mold, wherein thesecond plurality of injection ports is substantially aligned to a secondstraight line crossing the center, wherein the first straight line andthe second straight line are perpendicular to each other, and whereinthe second plurality of injection ports has sizes that are differentfrom each other.
 9. An apparatus comprising: a mold comprising: a topportion comprising a round edge; and an edge ring connected to the roundedge of the top portion, wherein the top portion and the edge ringdefine an inner space therein; a plurality of air vents penetratingthrough the edge ring of the mold, wherein the plurality of air ventshas different sizes; and a center injection port penetrating through thetop portion of the mold and connected to the inner space of the mold,wherein the center injection port is substantially aligned to a centerof the top portion of the mold.
 10. The apparatus of claim 9 furthercomprising a plurality of injection ports, wherein the center injectionport is one of the plurality of injection ports, wherein the pluralityof injection ports is substantially aligned to a straight line crossinga center of the top portion of the mold, and wherein the plurality ofinjection ports has different sizes.
 11. The apparatus of claim 10,wherein a size of a first air vent in the plurality of air vents issmaller than a size of a second air vent in the plurality of air vents,and wherein the first air vent is closer to the straight line than thesecond air vent.
 12. The apparatus of claim 9 further comprising apackage structure comprising a wafer, and a plurality of dies bonded tothe wafer, wherein the plurality of dies are inside the inner space. 13.The apparatus of claim 9 further comprising a molding dispenserconnected to the center port, wherein the molding dispenser isconfigured to inject a molding material into the inner space of themold.
 14. The apparatus of claim 13, wherein the molding dispensercomprises a controller configured to start injecting from a plurality ofinjection ports that is connected to the top portion of the mold atdifferent times.
 15. An apparatus configured to mold a wafer, whereinthe apparatus comprises: a mold comprising: a top portion having acenter; and an edge ring connected to a parameter of the top portion,wherein the edge ring comprises: an air vent; and a planar bottomconfigured to land on a top surface of the wafer; a plurality ofinjection ports penetrating through the top portion of the mold, whereinthe plurality of injection ports has different distances from the centerof the top portion of the mold, and the plurality of injection ports hasdifferent sizes; and a dispenser connected to the plurality of injectionports, wherein the dispenser is configured to inject a molding materialinto the mold through the plurality of injection ports.
 16. Theapparatus of claim 15, wherein a first one of the plurality of injectionports closer to the center of the top portion of the mold has a sizegreater than a second one of the plurality of injection ports fartheraway from the center.
 17. The apparatus of claim 15, wherein from thecenter to an edge of the top portion of the mold, the plurality ofinjection ports has increasingly smaller sizes.
 18. The apparatus ofclaim 15, wherein the dispenser is configured to start dispensing themolding material through different ones of the plurality of injectionports at different times.
 19. The apparatus of claim 15, wherein theedge ring comprises a plurality of air vents distributed with equaldistances.
 20. The apparatus of claim 9, wherein each of the pluralityof air vents is fully encircled by a material of the edge ring.